⚛️ Someone spent $420,000 porting TypeScript to Rust

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Theo spent over $420,000 in AI tokens trying to port the TypeScript compiler to Rust. Then he switched models, and the second one started from scratch and got further in a tenth of the time. Deno is joining Cloudflare, and the runtime only gets one more year of development. And someone took apart how ChatGPT's new interactive UI actually renders. It's not HTML.

Plus TanStack Start finally hit 1.0, a React Compiler prototype runs 51x faster, and Next.js is shipping a security fix today.

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Let's get into it.

💸 Someone Spent $420,000 Porting TypeScript To Rust
Theo set AI agents loose on porting the TypeScript 7 compiler to Rust. The first models burned over $400k in tokens, wrote 1.3 million lines, and stalled around 84% compatibility. Then he tried a different model. It threw everything out, started over, and got further in a tenth of the time. The README names the model, the final bill, and a confession: he's never read a line of the code. All 181,711 ported tests pass.

🔄 Your Users' Open Tabs Are Breaking Your Deploys
A backend engineer on an AI video app had users leaving tabs open for hours while the team kept deploying. The old build went looking for lazy-loaded chunks the deploy had already deleted, and got 404s. His fix wraps fetch to count open requests, then reloads stale tabs only when nothing is running. The comments are split. The most-upvoted replies say the fix is far simpler, and another warns that auto-reloading will make users hate you. The best story in there is a team that had to ship a "kamikaze" service worker to rescue one user stuck on a cached build six months later.

🦕 Deno Is Joining Cloudflare, And The Runtime Has One Year Left
The whole Deno team is moving to Cloudflare to work on Workers and Durable Objects. Deno Deploy shuts down in six months. The runtime gets a year of bug fixes and security patches, and then Deno stops developing it. Last week we ran David Bushell's "I'm back on Node" post. On Hacker News, Ryan Dahl himself asked "Why reimplement Node? It works."

🧩 How ChatGPT's Interactive UI Actually Works
GPT-6 can now answer with sliders, charts and forms, and someone reverse-engineered every layer. The model doesn't write HTML or JSON. It writes its own language, which gets compiled on the server and run somewhere you wouldn't expect. One detail: a single click in a pricing widget sent 158 UI updates, and four of them actually changed anything. It's by the team behind OpenUI, so they have a horse in this race, but it's a great teardown.

🚀 TanStack Start 1.0 Is Stable
The client-first alternative to Next.js is officially production-ready. Fortune 500 teams were running the beta, and Lovable and Netlify now use it by default for generated apps. The most interesting section is about RSC: Tanner supports it, built it, and then stopped using it on tanstack.com. His reason is worth reading.

⚡️ A React Compiler Prototype That's 51x Faster
Last week Jenna showed the compiler gets close to context selectors on its own. Jimmy Miller went further and prototyped the optimizations it doesn't do yet. Selecting a row in a 2,000-row list went from 254ms to 4.9ms. The twist: his first idea, inlining components, made things more than twice as slow, until he worked out what was missing.

🌳 Paste Your React Code, See Its Two Trees
Jules Blom built a playground that draws your component tree two ways: where output lands, and who rendered whom. Click any context provider or memo to see exactly what it covers. Paste the component you're scared of and see what's actually going on. Here's the notation behind it.

🚨 One 900 KB POST Froze A Next.js Server For 4 Seconds
A flaw in how React rebuilds form data for server actions turned one request into 100 million string checks. Behind a load balancer, three requests got the server pulled from rotation. It's fixed in React 19.0.6, 19.1.7 and 19.2.6. Separately, Next.js is shipping an out-of-band security update today for two Critical and one High vulnerability. Upgrade as soon as it's out.

🎟️ A Component Library With A Ticket You Can Tear
Ovio is a shadcn registry of 14 animated components for developer websites: contribution graphs, star history, npm downloads and sponsor walls. Each one comes in four styles (Minimal, Craft, Retro and Toy), and a couple are just for fun, like a physical knob and an event ticket you can actually tear off. Go tear the ticket. The Reddit thread has some sharp feedback on when playful interactions stop being fun.

💰 How Someone Found A $90,000 Bug In Google
A login cookie on developers.google.com was signed with a secret it was also carrying inside itself. Pulling that secret out let him forge sessions and run code on Google's servers with two GET requests. It worked on Firebase's and Android's docs sites too.

📡 Node Beat Bun And Deno At WebSockets
In 2023, Daniel Lemire found Bun twice as fast as Node. That result was wrong, because his Bun server had a bug. With a C client this time, Node 26 does 49,000 round trips a second against Deno's 40,000 and Bun's 37,000, close to a plain C relay.

🐦 Sindre Sorhus Dropped Astro. His Site Is Swift Now
Every page, component and style is Swift. Rename a page and every link to it stops compiling. A blog post ships at about 14 KB. Don't miss his 1999-style homepage, which has a guestbook you can sign.

🧱 className Considered Harmful
A Cloudflare design system maintainer on what happens after two years of teams passing className overrides into shared components. Atlassian's lint rule errors on any className at all. His fix is a scarier prop name you can grep for.

🖼️ A 9 MB WASM File Loaded 17% Faster Without Losing A Byte
Recraft's biggest file was requested last, behind three network round trips and a React tree. A preload hint and one function call moved it to the front. First render got 15–19% faster in an A/B test with 18k users per arm.

🧊 Freeze A Component While It Animates Out
Max Barvian found a way to stop exiting popovers from changing mid-animation: wrap them in Suspense, which renders but doesn't commit. The full component is 40 lines.

📱 React Native Web Is Moving To The React Foundation
Expo and zoontek are taking over maintenance. The plan drops React 18, moves from Flow to TypeScript, ships ESM only, and removes old components like CheckBox and Picker.

🎯 The Best Way To Use Icons In Web UIs
Lea Verou treats icons as CSS design tokens, inserted and tweaked with pseudo-elements, masks and style queries instead of a pile of SVG components.

Quick Links

🏥 Cockroach Labs Runs Its Coding Agents Like A Hospital
Agents play nurses, fellows and attendings, and no code gets written before a plan is reviewed. They shipped IBM Db2 support in under two days for $4,172 in tokens. The Oracle equivalent took nine months and about $160K. They also landed a million lines in five months with just seven reverts.

📋 38 Things PostHog Learned Building AI Products
5x more people use their MCP server daily than their own AI assistant. Their setup wizard turns two hours of work into about eight minutes, at $6.67 a run.

🛒 Why WebMCP Matters
Websites can hand agents real JavaScript tools instead of making them click around. In Shopify's checkout test it was 2.7x faster and 58% cheaper than browser automation. WebKit is opposed, and he explains why he disagrees.

🧑‍⚖️ When Code Is Cheap, Judgement Becomes The Job
Swizec's 21-person team auto-merges 16% of its PRs, and he does 40–50 code reviews a week. How the job actually changed, without the hype.

See you next week!

Darius